Authors: Wenming Tang Anqiang He Qi Liu Douglas G Ivey
Publish Date: 2008/02/27
Volume: 37, Issue: 6, Pages: 837-844
Abstract
Three Snrich AuSn alloy solders with eutectic hypoeutectic and hypereutectic Sn compositions were fabricated by sequential electroplating of Au and Sn and then the duallayer films were reflowed at 250°C The microstructures and phase compositions of the deposited Au/Sn duallayer film and the reflowed Snrich AuSn alloys were studied Microhardness values of the different phases or phase zones for the reflowed alloys were also tested Finally two Si wafers were bonded together with the eutectic Snrich AuSn alloy solder For as deposited Au/Sn duallayer films reaction between Au and Sn occurs at room temperature leading to the formation of Au5Sn AuSn and AuSn2 at the Au/Sn interface After reflowing at 250°C two phases remain Sn and AuSn4 with the morphology and phase distribution depending on the original solder composition In the Snrich eutectic AuSn alloy AuSn4 particles are distributed uniformly in the Sn matrix In the Snrich hypoeutectic/hypereutectic AuSn alloys the proeutectic phase AuSn4 Vickers hardness Hv 125 or Sn Hv 142 is larger in size and is surrounded by the eutectic zone Sn + AuSn4 Hv 161 In all cases the TiW adhesion and barrier layer remains intact during annealing After reflowing at 250°C under a pressure of 13 kPa two Si wafers are joined by the Snrich eutectic AuSn alloy solder without crack or void formation at the Si wafer/solder interface or within the solderThe authors wish to thank the Natural Sciences and Engineering Research Council NSERC of Canada and Micralyne Inc for providing research funding and Si substrates for electroplating Micralyne The first author would also like to thank the China Scholarship Council CSC and Hefei University of Technology China for financial support for studying abroad as well as the graduate students Weifeng Wei Chunfen Han and Nima Shaigan for their helpful discussion and cooperation
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